Sound like you are carrying too much speed?
The guys gave you the right advice, it's all about practice, and no throttle or wild turns on the wheel, highly recommend going on a weekday when the pressure is off. Lots of people get a boat drop it in the water and blast around all day, never practicing docking or loading, that mistake can make for lots of embarrassing and costly surprises and take a lot of the enjoyment out of boating.
Here's what I do... throttle down,... approach at about 45 degrees,with dock on the starboard /driver side of the boat,... as you get close shift to neutral, ...do not touch the throttle.....alternate short shifts in F the N as needed to control speed, slowly creep bow to dock on that 45 degree line....when bow is getting close, shift to N, and turn wheel ever so slightly away from dock....as it gets within a few inches, briefly shift to R, which should shed all speed and pull the stern toward the dock...then quickly back to N.
Of course, current and wind will be a factor, always stop and calculate these before beginning your approach, once you have a plan, time to set you bumpers. If your tendancy is to come in too hot, you could approach on the down wind side and let it help hold you off, but if you come up short, and need to throttle things can get hairy. Or you could stay upwind of the dock, approach very slow, align and allow the wind to push you toward the dock.
In all cases, if you practice staying off the throttle, keep the wheel straight, and alternate between F-N-R, you should be able to walk right up to the dock like a pro in no time.
Good luck, and happy boating!